<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item" 
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
         @click="handleLetterClick" >{{ item }}</li>
       
    </ul>
</template>
   
<script>
export default {
  name: "CityAlphabet",
  props: {
    cities: Object
  },
  computed: {
    letters() {
      const letters = [];
      for (let i in this.cities) {
        letters.push(i);
      }
      return letters;
    }
  },
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    };
  },
  updated() {
    this.startY = this.$refs["A"][0].offsetTop;
  },
  methods: {
    handleLetterClick(e) {
      this.$emit("change", e.target.innerText);
    },
    handleTouchStart() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if (this.touchStatus) {
        // const startY = this.$refs["A"][0].offsetTop;
        // console.log(startY);
        if (this.timer) {
          clearTimeout(this.timer);
        }

        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79;
          const index = Math.floor((touchY - this.startY) / 20);
          // console.log(index);
          if (index >= 0 && index < this.letters.length) {
            this.$emit("change", this.letters[index]);
          }
        }, 16);
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
};
</script>

<style lang="stylus" scoped >
@import '~styles/varibles.styl';

.list {
    display: flex;
    flex-direction: column;
    justify-content: center;
    position: absolute;
    top: 1.58rem;
    right: 0;
    bottom: 0;
    width: 0.4rem;

    .item {
        line-height: 0.4rem;
        text-align: center;
        color: $bgColor;
    }
}
</style>
